Which of the following devices extends the range of a network?

An access point is a networking hardware device that allows wireless devices to connect to a wired network using Wi-Fi or related standards. It helps extend the range of a wireless network by creating additional coverage areas. This is directly outlined in CompTIA ITF+ documentation:

“A wireless access point (AP) is a device that allows wireless clients to connect to a wired network. It serves to extend or broaden the wireless coverage.”

In contrast:

A modem connects to the internet via an ISP.

A server provides network services, not range.

A host firewall protects a single device or network; it does not expand connectivity.

Thus, the most appropriate answer is D.